Electrosurgery involves the use of an RF signal to produce electrosurgical effects, e.g., to cut, coagulate and/or desiccate. In conventional monopolar electrosurgery, an active electrode is contacted or positioned in close proximity to the tissue to be treated and a current return means (i.e. a pad) is positioned in contact with the patient to complete the circuit. Near the tip of the active electrode, the current is concentrated through a small area of tissue to provide a current density sufficient for cutting or coagulation. The current return means maintains a relatively large area of tissue contact to avoid tissue damage. If the contact surface of the current return means is too small, the current density may result in tissue damage.
In recent years, bipolar instruments have been used in certain electrosurgical applications. Bipolar instruments include a pair of closely spaced electrodes of opposite polarity, thereby eliminating the need for a remotely located current return means. It is an advantage of bipolar electrosurgical instruments that current flow is substantially restricted to a small area between the electrodes. Bipolar instruments thereby reduce the likelihood of current damage due to high local current densities or current flow through highly sensitive tissues. Thus, bipolar instruments are advantageously employed in applications such as neurosurgery where the adjacent tissue may be particularly susceptible to damage. Further ease-of-use advantages can be readily appreciated since bipolar instruments do not entail interconnection of a remotely located current return means.
Despite these advantages, bipolar instruments have suffered certain limitations. For example, certain bipolar instruments are not unitary, i.e., the electrodes are mounted on separate support structures. Surgeons using such instruments commonly operate one electrode with each hand. Such instruments, therefore, have the disadvantage that the surgeon may be left without a free hand during surgery. In addition, the use of two separate support structures may crowd the surgical site and limit the surgeon's view. Such instruments are also difficult to use in constricted areas and may therefore necessitate larger incisions.
Another limitation of known bipolar instruments is that such instruments may fail to reliably maintain electrode/tissue contact during surgery. In some known bipolar instruments, both of the electrodes are rigidly interconnected to a single support structure such that substantially constant spacing is maintained between the electrodes. When such instruments are used in an area of irregular tissue topography, one or both of the electrodes may occasionally lose contact with the tissue due to the inability to move the electrodes independently, resulting in unsatisfactory instrument performance.
Similarly, certain bipolar instruments have been limited due to the inability to easily and adequately adjust the cutting depth of such instruments during surgery. For example, one type of bipolar instrument employs a single cutting electrode and a second current return means positioned a substantially fixed distance rearwardly of the cutting electrode. In practice, a surgeon's ability to control the cutting depth of such instruments is hampered due to the inability to easily vary the distance between the cutting electrode and the current return means during surgery.
In addition, known bipolar instruments have generally not been adapted for general use in cutting, coagulation and desiccation modes. The electrosurgical effect achieved can be varied by changing the signal provided by an electrosurgical generator. For example, a continuous sinusoidal signal waveform generally is used for cutting while an interrupted waveform is used for coagulation. Presently, many bipolar instruments are principally employed to coagulate using the interrupted coagulation signals. Indeed, electrosurgical generators often have separate outlets for interfacing with monopolar and bipolar instruments and the cut signal option is often not even available via the bipolar outlet. It is therefore common for surgeons to use separate instruments for cutting and coagulation, resulting in time consuming double handling during surgery. Other bipolar instruments produce electrosurgical effects at both of the electrodes, thereby affecting the surgeon's ability to accurately limit the area of tissue to be acted upon.
Moreover, many challenges remain with respect to realizing the full potential of bipolar electrosurgical instruments for minimally invasive internal surgical procedures such as laparoscopic surgery. Such minimally invasive procedures, which normally involve accessing the surgical site through a narrow tube or cannula, are increasingly popular because they can avoid the need for large incisions, thereby reducing patient scarring and trauma. However, the spatial limitations inherent in such settings place practical limits on the dimensions and configuration of the electrodes utilized and can make it difficult to maintain adequate electrode/tissue contact for certain procedures. Additionally, in designing electrosurgical instruments for use in such constricted environments, special care must be taken to reduce the likelihood of producing undesired electrosurgical effects due to inadvertent tissue contact, e.g., inadvertent contact between exposed active electrode portions and tissue adjacent to the surgical site. A further consideration in designing such instruments is that the surgeon's view of the surgical site, which is typically limited during minimally invasive internal procedures, should not be unduly obstructed. Presently, it appears that no one has succeeded in providing a bipolar electrosurgical instrument for use in a variety of minimally invasive procedures which meets the needs of the industry.